Near-Infrared Light Propagation in an Adult Head Model. II. Effect of Superficial Tissue Thickness on the Sensitivity of the Near-Infrared Spectroscopy Signal

Department of Electronics and Electrical Engineering, Keio University, Edo, Tōkyō, Japan
Applied Optics (Impact Factor: 1.78). 07/2003; 42(16):2915-22. DOI: 10.1364/AO.42.002915
Source: PubMed


It is important for near-infrared spectroscopy (NIRS) and imaging to estimate the sensitivity of the detected signal to the change in hemoglobin that results from brain activation and the volume of tissue interrogated for a specific source-detector fiber spacing. In this study light propagation in adult head models is predicted by Monte Carlo simulation to investigate the effect of the superficial tissue thickness on the partial optical path length in the brain and on the spatial sensitivity profile. In the case of source-detector spacing of 30 mm, the partial optical path length depends mainly on the depth of the inner skull surface whereas the spatial sensitivity profile is significantly affected by the thickness of the cerebrospinal fluid layer. The mean optical path length that can be measured by time-resolved experiments increases when the skull thickness increases whereas the partial mean optical path length in the brain decreases when the skull thickness increases. These results indicate that it is not appropriate to use the mean optical path length as an alternative to the partial optical path length to compensate the NIRS signal for the difference in sensitivity caused by variation of the superficial tissue thickness.

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    • "The near-infrared light sources, which are laser-emitting diodes, are placed directly onto a participant's scalp and are sent—in a “banana-shaped” form (Okada and Delpy, 2003)—to the detectors, called optodes. The depth and exactness of measurement depends on the distance between the source and the detector. "
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    Frontiers in Human Neuroscience 08/2014; 8:549. DOI:10.3389/fnhum.2014.00549 · 3.63 Impact Factor
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    • "Considering this aim, we hypothesized that the PFC would be the most suitable measurement location, since it is easier accessible using fNIRS as compared to S2 (due to coverage by hair) or ACC (due to too high cortical depth) (Haeussinger et al., 2011; Huppert et al., 2007; Okada & Delpy, 2003). "
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